Our new enhancement for our hosted sql-ledger allows you to make any invoice line item non-taxable regardless of its customer/item settings.
Following screen shots explain this feature:
The Tx checkbox is checked by default and the line item tax is calculated according to customer/item settings.
When you un-check the Tx checkbox, tax is not calculated for the line item.
This enhancement is optional and you can request to install it into your hosting instance by submitting a support ticket to firstname.lastname@example.org.